The long-range goal of this research is to promote an understanding of the mechanisms by which a eukaryote cell, starting with genetic material, manages to synthesize gene products. The particular gene products to be studied here are yeast tRNAs. The proposed research program is directed towards determining: a) the organization of tRNA genes on the yeast chromosome; b) the relationship of an original tRNA transcript to a final mature tRNA; c) and, the biochemical steps involved in the maturation of the initial transcript to a functional tRNA. The overall rationale of this work is that the identification and characterization of mutants defective in tRNA biosynthesis is the most direct approach to understanding those processes which are important in tRNA transcription and maturation. To date we have identified one mutant (ts 136) which accumulates approximately 12 species of precursor tRNA. Some of these species have transcrived intervening sequences (Knapp et al., in preparation). We will continue to characterize the precursor tRNAs which accumulate in ts 136. We are also attempting to isolate yeast mutants which are conditionally defective in suppression of nonsense mutations; some of these mutants should be defective in tRNA transcription and/or maturation.